This module simplifies manipulation with MiniMagick by providing a set of convenient helper methods. If you want to use them, you’ll need to require this file: 

    require 'carrierwave/processing/mini_magick'

And then include it in your uploader: 

    class MyUploader < CarrierWave::Uploader::Base
      include CarrierWave::MiniMagick
    end

You can now use the provided helpers: 

    class MyUploader < CarrierWave::Uploader::Base
      include CarrierWave::MiniMagick

      process :resize_to_fit => [200, 200]
    end

Or create your own helpers with the powerful manipulate! method. Check out the ImageMagick docs at www.imagemagick.org/script/command-line-options.php for more info 

    class MyUploader < CarrierWave::Uploader::Base
      include CarrierWave::MiniMagick

      process :do_stuff => 10.0

      def do_stuff(blur_factor)
        manipulate! do |img|
          img = img.sepiatone
          img = img.auto_orient
          img = img.radial_blur blur_factor
        end
      end
    end

Note

MiniMagick is a mini replacement for RMagick that uses the command line tool “mogrify” for image manipulation.

You can find more information here:

mini_magick.rubyforge.org/ and github.com/probablycorey/mini_magick/

Methods
C
I
M
R
Classes and Modules
Class Public methods
included(base)

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 60
    def self.included(base)
      super
      base.extend(ClassMethods)
    end
Instance Public methods
convert(format)

Changes the image encoding format to the given format

See www.imagemagick.org/script/command-line-options.php#format

Parameters

format (to_s)
an abreviation of the format

Yields

MiniMagick::Image
additional manipulations to perform

Examples

    image.convert(:png)

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 104
    def convert(format)
      manipulate! do |img|
        img.format(format.to_s.upcase)
        img = yield(img) if block_given?
        img
      end
    end
manipulate!()

Manipulate the image with RMagick. This method will load up an image and then pass each of its frames to the supplied block. It will then save the image to disk.

Gotcha

This method assumes that the object responds to current_path. Any class that this module is mixed into must have a current_path method. CarrierWave::Uploader does, so you won’t need to worry about this in most cases.

Yields

MiniMagick::Image
manipulations to perform

Raises

CarrierWave::ProcessingError
if manipulation failed.

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 255
    def manipulate!
      image = ::MiniMagick::Image.from_file(current_path)
      image = yield(image)
      image.write(current_path)
      ::MiniMagick::Image.from_file(current_path)
    rescue ::MiniMagick::MiniMagickError => e
      raise CarrierWave::ProcessingError.new("Failed to manipulate with MiniMagick, maybe it is not an image? Original Error: #{e}")
    end
resize_and_pad(width, height, background=:transparent, gravity='Center')

Resize the image to fit within the specified dimensions while retaining the original aspect ratio. If necessary, will pad the remaining area with the given color, which defaults to transparent (for gif and png, white for jpeg).

See www.imagemagick.org/script/command-line-options.php#gravity for gravity options.

Parameters

width (Integer)
the width to scale the image to
height (Integer)
the height to scale the image to
background (String, :transparent)
the color of the background as a hexcode, like “ff45de“
gravity (String)
how to position the image

Yields

MiniMagick::Image
additional manipulations to perform

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 218
    def resize_and_pad(width, height, background=:transparent, gravity='Center')
      manipulate! do |img|
        img.combine_options do |cmd|
          cmd.thumbnail "#{width}x#{height}>"
          if background == :transparent
            cmd.background "rgba(0, 0, 0, 0.0)"
          else
            cmd.background background
          end
          cmd.gravity gravity
          cmd.extent "#{width}x#{height}"
        end
        img = yield(img) if block_given?
        img
      end
    end
resize_to_fill(width, height, gravity = 'Center')

From the RMagick documentation: “Resize the image to fit within the specified dimensions while retaining the aspect ratio of the original image. If necessary, crop the image in the larger dimension.“

See even www.imagemagick.org/RMagick/doc/image3.html#resize_to_fill

and

www.clipclip.org/clips/detail/4365/jerrett-net-»-crop_resized-in-rmagick

Parameters

width (Integer)
the width to scale the image to
height (Integer)
the height to scale the image to

Yields

MiniMagick::Image
additional manipulations to perform

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 180
    def resize_to_fill(width, height, gravity = 'Center')
      manipulate! do |img|
        cols, rows = img[:dimensions]
        img.combine_options do |cmd|
          if width != cols || height != rows
            scale = [width/cols.to_f, height/rows.to_f].max
            cols = (scale * (cols + 0.5)).round
            rows = (scale * (rows + 0.5)).round
            cmd.resize "#{cols}x#{rows}"
          end
          cmd.gravity gravity
          cmd.extent "#{width}x#{height}" if cols != width || rows != height
        end
        img = yield(img) if block_given?
        img
      end
    end
resize_to_fit(width, height)

From the RMagick documentation: “Resize the image to fit within the specified dimensions while retaining the original aspect ratio. The image may be shorter or narrower than specified in the smaller dimension but will not be larger than the specified values.“

See even www.imagemagick.org/RMagick/doc/image3.html#resize_to_fit

Parameters

width (Integer)
the width to scale the image to
height (Integer)
the height to scale the image to

Yields

MiniMagick::Image
additional manipulations to perform

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 152
    def resize_to_fit(width, height)
      manipulate! do |img|
        img.resize "#{width}x#{height}"
        img = yield(img) if block_given?
        img
      end
    end
resize_to_limit(width, height)

Resize the image to fit within the specified dimensions while retaining the original aspect ratio. Will only resize the image if it is larger than the specified dimensions. The resulting image may be shorter or narrower than specified in the smaller dimension but will not be larger than the specified values.

Parameters

width (Integer)
the width to scale the image to
height (Integer)
the height to scale the image to

Yields

MiniMagick::Image
additional manipulations to perform

Source: show | on GitHub 

# File lib/carrierwave/processing/mini_magick.rb, line 127
    def resize_to_limit(width, height)
      manipulate! do |img|
        img.resize "#{width}x#{height}>"
        img = yield(img) if block_given?
        img
      end
    end